It is common in aircraft with Fly-By-Wire (FBW) Flight Control Systems that they are designed to protect against both random failures and design errors. Protection against random failures is generally achieved by using redundant channels of equipment. The flight control system generally provides a normal mode that uses redundant channels of inertial signals, such as provided by a micro electromechanical system (MEMS) attitude and heading reference systems (AHRS) or an Inertial Reference System (IRS). Each AHRS or IRS has three gyroscopes and three accelerometers and a microprocessor with software to calculate a full complement of inertial signals. The complexity of the microprocessor and software causes such signals to be susceptible to hardware or software errors, and they are generally considered to be not fully analyzable for design errors.
Protection against design errors is generally achieved by augmenting the flight control normal mode with a simpler backup mode that can be activated in the event of a design error in the normal mode. The backup mode requires a subset of inertial signals (generally only body rate signals) that are simpler in design and hence are fully analyzable against design errors. The inertial signals for the backup mode generally have relaxed accuracy requirements compared to the signals for the normal mode. The backup mode inertial sensors are also generally redundant to protect against random failures. This means the flight control system requires duplicate sets of redundant inertial sensors—one set for the normal mode and another set for the backup mode. This duplication of inertial sensors increases the cost of the flight control system.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an effective and efficient control signal system.